Summary

I love the double start bolt and nuts from JDubs55303.

As an engineer, my only gripe was that the nuts were just plain cylinders. So this design takes the originals and encloses them in a hexagonal nut.

Printing in colour changing PLA works well and adds to the fun. :)

(I'd like to adjust the bolt design to have a chamfered head, to match the nuts. Trouble is that the bolt STL isn't manifold, so OpenScad can't work with it properly and I haven't taken the time to sort this out (yet).)